1. Field of the Invention
The present invention relates to a method of assembling an inner diameter grinding tool which precisely grinds the inner surface of a hole formed in a workpiece by a drill or the like.
2. Description of the Related Art
As a tool for grinding the inner diameter of a crank journal bearing that is formed by combining a cylinder block and a lower block, a tool having a roughing cutter, a semi-finishing cutter, and a finishing cutter provided axially in series and on the same axis line has been proposed in Japanese Patent Laid-Open No. 2007-090450.
In the tool disclosed in Japanese Patent Laid-Open No. 2007-090450, the projecting amount of the cutter in the radial direction of the tool cannot be adjusted. Thus, when a plurality of portions to be machined are ground at the same time, the tool body (an arbor) interferes with a workpiece. To solve the problem, a machining tool where the radial projecting amount of a cutter can be adjusted has been proposed in Japanese Patent Laid-Open Nos. 2003-165021 and 2005-14175.
Japanese Patent Laid-Open No. 2003-165021 discloses a reamer in which a plurality of rectangular concave portions are formed in the outer periphery of a holder, a blade (a grindstone) is housed in each of the concave portions, a slider having a conical portion is provided in the hollow cylinder of the holder, and the slider is moved to adjust the radial length of the blade, as a conventional example.
Japanese Patent Laid-Open No. 2003-165021 also discloses a structure in which a slit is provided at a position close to the outer peripheral surface of the blade between both the ends in the longitudinal direction thereof, a rectangular through hole is formed perpendicular to and including the slit, and a shim is inserted into the through hole, to thereby finely adjust the radial length independently with respect to each of the blades, as an improved example of the conventional example.
Furthermore, Japanese Patent Laid-Open No. 2005-14175 discloses a structure as below. An abrasive grain portion is formed on the outer peripheral surface of a cylindrical portion of a grindstone body by fixing abrasive grains thereon. A chamfered corner portion inclined toward the edge such that the diameter becomes smaller, and a machining dimension finishing portion are formed at an end portion of the abrasive grain portion. The end portion of the abrasive grain portion is also cut in a staggered shape with a first slit and a second slit extending in the axial direction, to form a parallel expansion portion on the abrasive grain portion. A tapered hole is formed in the inner peripheral surface of the cylindrical portion over the entire length of the parallel expansion portion of the abrasive grain portion. A tapered cone is fitted into the tapered hole. By axially adjusting the position of the tapered cone, the parallel expansion portion of the abrasive grain portion is parallelly expanded.
When a tool not capable of extending the radial length of a grinding section machines a workpiece having a plurality of portions to be machined such as a crank journal bearing at the same time, the tool interferes with the workpiece.
Even if a tool capable of extending the radial length of a grinding section is used, the center of a draw bar is misaligned from the center of a tool holder in the vicinity of a distal end portion as shown in FIGS. 7(A) and 7(B) when the axial length of the grinding section is extended, the axial length of the tool holder holding the grinding section is thus extended, and the draw bar inserted into the tool holder is also lengthened. As a result, only a specific grinding section out of a plurality of grinding sections grinds the workpiece, thereby causing uneven wearing, or deterioration in surface accuracy and machining accuracy with the draw bar moving erratically in the tool holder during rotation.
To solve the problem, the tool holder includes a plurality of axially divided tool holders, so that each of the divided tool holders is relatively easily aligned with the center of the tool holder. However, it becomes difficult to accurately obtain the coaxiality of the inner diameter of the tool holder at the time of assembling the divided tool holders.